Research In Mmc Distributed Control System Based On Communication Technology

With rapid development of power semiconductor devices,communication and control technologies,the mankind gets huge advance in the filed of power electronics converter system.Specifically,power density,power capacity and control functions gain a nice all-around performance boost.Modular multilevel converter(MMC)is recognized as the most promising,most efficient and widely used power electronics topology in the field of flexible DC power transmission.For a large-capacity power electronic converter system such as MMC,there are a large number of switching devices,feedback and control variables in the system.If traditional centralized control architecture and methods are still used,communications efficiency and system modularity will not be desirable,which brings poor reliability and versatility.Compared with centralized control system,distributed control system has distinguished advantages.Its modularity,standardization,high reliability,high power density,maintainability and scalability are corresponded with characteristic of modern power electronics technology.In addition,MMC has a high level demand for real-time control,and has obvious distributed characteristics in the aspect of control functions and circuit structures.Therefore,this paper focus on the MMC distributed control system based on optical fiber communication technology.The main research contents are as follows:First of all,the article deduces some theoretical formulas,such as ripple voltage and ripple current of sub-module capacitor,power loss of switching devices,and inductor ripple current,and then discuss the situation of worst performance of each component design.As a result,the article provides the related guidance for choosing elements and designing circuit.Secondly,aiming at the problems existing in the traditional control method of MMC,the carrier phase shift PWM control strategy and the principle of capacitor voltage balance algorithm are proposed,and the article analyzes the reasons why the carrier phase shift PWM control strategy is suitable for distributed control.A 17-level MMC inverter system model was built based on MATLAB / Simulink,and simulation analysis was performed to verify the effectiveness of the control strategy and voltage balance algorithm.Then,for problems of the MMC traditional architecture,such as optical fiberconsume,optical modules-consume,complicated communication systems design,and asynchronous sub-modules,the idea of passive optical fiber network system is applied to the design of MMC control system,and an architecture of MMC distributed control system based on optical splitter is proposed.The whole system is composed of main controller,phase controller,sub-module controller and optical splitter.Between the phase controller and the sub-module controller,a downlink broadcast method and an uplink time division multiplex technology are used to provide data transmission,meanwhile each controller is responsible for their own work.At last,based on GTP high-speed serial transceiver pins provided by the FPGA,Aurora protocol integrated core and AXI4 data flow protocol,the SFP optical modules and optical splitters are used to connect.An experiment platform of high-speed information interaction between MMC controllers is designed,offering and further confirming the possibility of MMC distributed control system based on optical splitter.